The present invention pertains generally to the field of radio frequency (RF) power transistor devices and, more specifically, to high frequency, high power signal amplifiers used in wireless communication applications.
The use of RF power transistor devices as signal amplifiers in wireless communication applications is well known. With the recent growth in the demand for wireless services, such as personal communication services, the operating frequency for wireless networks has increased dramatically and is now well into the gigahertz. For example, RF power transistors are commonly used in amplification stages for radio base station amplifiers in wireless communication networks. Such power transistors are also widely used in other RF-related applications, such as cellular telephones, paging systems, navigation systems, television, avionics, and military applications.
Production of RF power transistors on a large-volume basis is traditionally problematic, because of natural variables that the individual transistor elements possess. For example, the transistor devices have natural variances in input capacitance, gain and phase shift. In commercial implementations, significant time and effort is needed to first characterize a particular transistor device over a range of expected operating frequencies and voltages, and then attempt to build further devices using like materials, which deliver similar desired performance. Due to the variations in transistors"" and various other elements over identical operating frequencies and voltages, however, the ability to successfully tune transistor devices on a large scale manufacturing basis is limited.
Such problems with large scale manufacturing of power transistor devices and amplifiers in high frequency applications are compounded by ever widening operating power ranges and very broad bandwidths of evolving wireless applications, such as those required in a Third Generation (xe2x80x9c3Gxe2x80x9d) wireless network. In particular, input and output impedance matching becomes very difficult over such wide power ranges and high frequencies, and even small variations in device construction can cause instability and failure.
In accordance with a general aspect, inventions disclosed and described herein are directed to high frequency, high power (hereinafter xe2x80x9cbroadbandxe2x80x9d) RF signal amplifiers designed and constructed to overcome the above-described problems, and allow for easier large-scale manufacturing and uniform performance.
In one embodiment, the broadband RF amplifier includes a plurality of power transistors attached to a surface of a pedestal, each transistor having an input and an output. A RF input path electrically connected to the respective transistor inputs includes a passive splitter implemented in a multi-layer printed circuit board (xe2x80x9cPCBxe2x80x9d) and configured to split a RF input signal into a plurality of component input signals. A corresponding plurality of input matching networks employing one-quarter wavelength transmission lines implemented in the PCB couple the respective component input signals to the transistor inputs at an input impedance. A RF output path electrically connected to the respective transistor outputs includes a passive combiner implemented in the PCB and configured to combine component output signals at the transistor outputs into a RF output signal. A corresponding plurality of output matching networks employing one-quarter wavelength transmission lines implemented in the PCB couple the respective component output signals at the transistor outputs to an output impedance.
In one embodiment, the PCB has an opening sized to accommodate the pedestal, such that respective input and output reference ground shelves implemented in the PCB are located adjacent a pedestal surface to which the power transistors are attached. Respective sets of bond wires electrically connect the input and output reference ground shelves to the pedestal surface, the input and output reference ground shelves and the pedestal surface positioned sufficiently close that the bond wires provide relatively low inductance transmission paths.
By splitting the RF input signal into individually amplified component, which are then combined, the operating point of each transistor may be relatively low, allowing for the input impedance at each transistor to be relatively high. This, in turn, provides for greater stability through the full operating range of the broadband amplifier, which still providing the requisite performance characteristics. A preferred embodiment of the broadband amplifier is efficiently achieved by implementing the input and output matching and direct current bias networks in a multi-layer PCB module. Transmission lines of the respective matching and bias networks are coupled to power transistors located on a separate pedestal sharing a common reference ground with the PCB.
Other aspects and features of the inventions disclosed herein will become apparent hereinafter.